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THE 19TH
INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS
1 Introduction
The fabrication of continuous fiber
reinforced thermoplastic composite involves two
problems. The first one is that thermoplastics as
matrices generally have high melt viscosity so that
it is difficult to impregnate resin into reinforcing
fiber bundle. To overcome this problem, micro-
braided yarn (MBY) with CF and thermoplastic
fiber have been developed as an intermediate
material by Japanese traditional braiding technique
as shown in Fig. 1. MBY is fabricated by braiding
resin fibers alongside reinforcement fiber. Since
resin fibers are located close to reinforcement fiber
bundle, impregnation performance of
thermoplastics is excellent [1].
The other one is low interfacial properties
between the fiber and matrix. It is considered that
interfacial properties in continuous fiber reinforced
thermoplastic composites can be characterized by
the wetting ability and chemical interaction
between fiber and matrix. Wetting ability would
affect resin impregnation state during molding
while chemical reaction affects composite strength.
Therefore, interface design of CFRTP is very
important to obtain composite materials with
improved processability and mechanical
performance.
In our previous research [2], it has been
clarified that the CF/PP had good impregnation
property but low interfacial strength in the
composite performance. On the other hand,
CF/MAPP had low impregnation property but high
interfacial strength in the composite.
The objective of this research is to improve
the both impregnation state and interfacial shear
strength by using surface treatment on carbon fiber.
To achieve this objective, low molecular
weight Polypropylene (L-PP) and non-ionic
Polypropylene emulsifying agent (PP-emulsion)
were used.
2 Fabrication Method
The materials used in this study were carbon
fiber as the reinforcement (T700SC-12000 Toray
Co., ltd), and polypropylene (PP) and maleated
polypropylene (MAPP) fibers as matrix resin.
To evaluate interfacial shear strength of the
CF/PP or MAPP, the micro-droplet test was
employed. The CF was treated by using L-PP and
PP-emulsion with various concentrations at 0, 0.6,
1.4, 2.5, 3.5, and 8.0wt%.
To evaluate the impregnation state and
mechanical properties of the composite, the CF/PP
or MAPP composites were fabricated. A tubular
braiding machine was used for fabricating MBY as
an intermediate material for producing
unidirectional continuous fiber reinforced
thermoplastic composites [3, 4]. CF as the
reinforcement fibers untreated and treated with L-
PP or PP-emulsion was aligned vertically and
braided with PP or MAPP fiber to yield CF/ PP or
MAPP MBY by using a technique known as micro
braiding. These MBYs were later used to prepare
composites.
IMPROVEMENT OF IMPREGNATION AND MECHANICAL
PROPERTIES OF CFRTP COMPOSITES
BY MICRO-BRAIDED YARNS
P. Wongsriraksa1*, A. Nakai
2, K. Uzawa
1 and I. Kimpara
1
1 Research Laboratory for Integrated Technological Systems, Kanazawa Institute of Technology,
Hakusan, Ishikawa Prefecture, JAPAN, 2 Department of Mechanical Engineering, Gifu University, Gifu, JAPAN
* Corresponding author ([email protected])
Keywords: Impregnation, CFRTP, Mechanical properties, Micro-Braided yarn, Micro-Droplet.
Prior to compression molding process for
fabricating the composites, the MBYs were wound
onto a parallel metallic frame with a size of
20×340mm equipped with a spring mechanism to
prevent thermal shrinkage during molding, as
shown in Fig. 2. The wound frame was then placed
into a pre-heated mold with a size of 20×200mm
and compression molding was performed at 200C
with a molding pressure of 10 MPa for 60 minutes.
Cooling was subsequently performed by running
water through the mold while keeping the
specimens under constant pressure.
4 Testing Method
Micro-droplet test was performed to
investigate interfacial adhesion and the interfacial
shear strength of the CF/PP or MAPP interface was
examined. The resin fiber was melted by using a
hot plate at 220oC and a small droplet of resin was
applied to a single fiber. Micro-droplet test machine
HM410 (Tohei Sangyo Co.,Ltd ) was used with a
fiber pull-out speed of 0.03 mm/min. When the
micro-droplet touches the knife edges, the interface
is solicited in shear mode. The maximum load F
measured before matrix detachment from the fiber
is related to the fiber/matrix shear strength. The
interfacial shear strength (τ) was calculated by
equation 1,
dl
F
(1)
where F is the maximum load, d is the fiber
circumference, and l is the embedded fiber length.
The values of the fiber circumference and
embedded length were characterized using
microscope images as shown in Fig.3.
The wetting ability with contact angle was
examined to investigate wetting ability of the
CF/PP or MAPP. The resin fiber and CF filament
were put on glass slide and it was melted by using a
hot plate at 200oC. The resin fiber in melting was
observed by using microscope as shown in Fig. 4.
The surface of specimens after micro-droplet
was observed by scanning electron microscope
(SEM). The specimens were dried and gold coated
by using a sputtering machine (JEOL, JFC-1100E)
for 8 minutes to make the surface electrically
conducting, in order to prevent accumulation of
electron charges on the specimen surface during
observation. The coated specimens were observed
by using a scanning electron microscope (JEOL
5400).
In order to observe the impregnation state of
the composite, the cross-section of CF/PP or MAPP
composites were polished and observed by using an
optical microscope OLYMPUS-PME3 (IC5).
For the mechanical property, 3-point bending
test of unidirectional composites was performed by
using an INSTRON universal testing machine
(model 4206). The specimen size was 50mm in
length, 15mm in width and 1.5~1.8 mm in thickness.
The span length was 25mm and the test speed was
1mm/min.
5 Results and Discussion
Fig.5 shows relationship between interfacial
shear strength of CF/PP or MAPP and content of
surface treatment. In the case of CF/PP with L-PP,
the interfacial shear strength was increased until
0.6% and then decreased with increase in the
surface treatment content. While surface treatment
with PP-emulsion, the interfacial shears strength
was increased until 1.4% and then kept constant
value with increase in the surface treatment content.
In the case of CF/MAPP, the interfacial shear
strength was decreased until 3.5% and then kept
constant value for both L-PP and PP-emulsion. In
the case of CF/PP and CF/MAPP treated with PP-
emulsion, the interfacial strength was higher than
that treated with L-PP.
Fig. 6 shows SEM photographs after micro-
droplet test for 2.1wt%. After the micro-droplet test
specimen of CF/MAPP, the breaking point of the
resin had larger damage more than CF/PP. It
indicated that CF/MAPP has high interfacial shear
strength more than CF/PP.
Fig. 7 shows the wetting ability by contact
angle of CF/PP and CF/MAPP with untreated and
treated with L-PP and PP-emulsion at 2.1wt%. In
the case of untreated specimens, the contact angle
of CF/MAPP was bigger than that CF/PP. In the
case of CF/PP treated with L-PP, the contact angle
was not changed when compare with untreated
specimen but bigger than treated with PP-emulsion.
While in the case of CF/MAPP treated with L-PP,
the contact angle was decreased when compare with
untreated specimen from 96° to 39° and still bigger
than treated with PP-emulsion. In the case of CF
treated with L-PP and PP-emulsion, the contact
angle of CF treated with L-PP was bigger than CF
treated with PP-emulsion. It indicated that the
wetting ability of CF treated with L-PP was lower
than CF treated with PP-emulsion.
Fig. 8 shows the impregnation state by cross-
sectional photographs of composites by untreated
and treated with L-PP and PP-emulsion. In the case
of untreated specimens, the impregnation ratio of
CF/PP was higher than CF/MAPP. In the case of
CF/PP, the impregnation ratio was slightly
decreased by L-PP. While in the case of CF/PP
treated with PP-emulsion, impregnation ratio was
100% as same as untreated one, moreover, the
fibers were highly dispersed compare with
untreated one. In the case of CF/MAPP, the
impregnation ratio was increased by L-PP and
became 100% by PP-emulsion.
Fig.9 shows the bending strength of
composites. In the case of untreated specimen, the
bending strength of CF/PP was much lower than
CF/MAPP. The strength of CF/PP was drastically
improved by surface treatment and the increasing
ratio by PP-emulsion was higher than that by L-PP.
In the case of CF/MAPP, the strength was slightly
improved by the surface treatment.
Fig. 10 shows the SEM photographs of
surfaces of composites after bending test. In the
case of CF treated by PP-emulsion, the amount of
resin sit on fiber much more than CF untreated and
treated by L-PP. This is an indication of strong
interfacial adhesion between CF and the matrix.
From these results in the case of CF/PP, CF
treated with PP-emulsion could improve the
interfacial strength between fiber and resin and
bending strength of composites. In the case of
CF/MAPP, CF treated with PP-emulsion could
improve the impregnation of the resin into fiber
bundle by increasing the wetting ability and
improve the bending strength of composites. It
indicated that CF treated with PP-emulsion could
produce composites with better mechanical
performance.
6 Conclusions
The surface treatment by Low-PP and PP-
emulsion was effective both for CF/PP and
CF/MAPP in the impregnation properties and the
interfacial properties for CF/PP composites. It was
established that surface treatment by Low-PP and
PP-emulsion could produce composites with better
mechanical properties for CF/PP and CF/MAPP.
References
[1] Y. TAKAI, N. KAWAI, A. NAKAI and H.
HAMADA “Effect of Resins on Crack
Propagation of Long-Fiber Reinforced
Thermoplastic Composites”, Design,
Manufacturing and Applications of Composites,
Toronto, Canada, pp. 196-202, DEStech
Publications,Inc., 2006.
[2] Yoshitaka Tanaka, Hajime Nakamura, Akio
Ohtani, Nobuo Ikuta and Asami Nakai, “Effect
of interfacial property on CF/PP continuous
fiber reinforcement thermoplastic composite”,
Design, Manufacturing and Applications of
Composites, Quebec, Canada, pp. 277-285,
DEStech Publications,Inc., 2010.
[3] M SAKAGUCHI, A NAKAI, H
HAMADA, and N TAKEDA, Compos Sci
Technol, 717-722 (2006).
[4] O.A. KHONDER, U.S. ISHIKAKU, A.
NAKAI, and H. HAMADA, Composites Part
A: applied science and manufacturing, 2274-
2284 (2006).
Reinforcing fiber bundle
Matrix resin fiber
Reinforcement fiber bundle
Matrix resin fiber
Fig. 1 Fabrication of Micro-braided yarn (MBY)
Die
Metallic frame
SpringCompression
moldingCentral fiber (CF)
Braiding yarn (PP fiber)
Molding press:10 MPa, Molding temperature:200℃,
Molding time:5, 10, 20, 40 min
Fig. 2 Fabrication method of unidirectional specimens
FiberFiber diameter, d
Embedded Fiber length, l
To load cell
Fig. 3 Micro-droplet test
Hot plateTemperature:200℃
Micro scope
Carbon fiber
PP fiberResin area
Fig. 4 Wetting ability by contact angle test
0
2
4
6
8
10
12
14
16
18
20
0 2 4 6 8
Inte
rfa
cia
l sh
ear
stre
ng
th
(MP
a)
Surface treatment content (wt%)
L-PP-PP
L- PP-MAPP
PP-emulsion-PP
PP-emulsion-MAPP
Fig. 5 Relationship between interfacial shear strength of CF/PP or MAPP and surface treatment content.
CF/PP
CF/MAPP
moving direction of resin
Untreated L-PP PP-emulsion
Fig. 6 SEM photographs of micro-droplet test
CF/PP
CF/MAPP
22°
CF
Resin area0-1°
25°
Untreated L-PP PP-emulsion
0-1°
Fig. 7 Photographs of contact angle
CF/PP
CF/MAPP
L-PP PP-emulsion Untreated
Impregnation 100% Impregnation 97%
Impregnation 60% Impregnation 79%
Impregnation 100%
Impregnation 100%
Fig. 8 Cross sectional photographs of composites.
0
50
100
150
200
250
300
350
400
450
500
CF/PP CF/MAPP
Ben
din
g s
tren
gth
(M
Pa
) Untreated
L-PP
PP-emultion
Fig. 9 Bending strength of composites
100µm 100µm
100µm
100µm 100µm
100µm
CF/PP CF/MAPP
L-PP
PP-emulsion
Untreated
Fig. 10 SEM photographs of surfaces of composites